senthilp/cachewarmer

A JavaScript utility to warmup cache and maximize cache usage

CacheWarmer

CacheWarmer is built on the concept of using browser idleness as a playground to pre-fetch and cache resources that users will be needing later. If browser supports Web Workers then a worker thread is spawned which takes care of all the resource caching.

It is a JavaScript utility to pre-fetch and cache resources/data on the client side or execute JavaScript functions in small periodic chunks without penalizing UI responsiveness or user interactions (similar to webwrokers, but work in all browsers). This will be extremely useful for applications to retrieve data before hand and respond immediately when data is requested.

Typical use cases would be pre-fetching JS/CSS resources which will be required for upcoming pages or other on-demand functionalities, data that needs to be fetched (through AJAX etc.) based on user actions, messages in email applications etc.

The key challenge here is the single threaded nature of JavaScript in which the same thread is shared between UI rendering and interactions. The CacheWarmer utility simulates a multi-threaded browser environment using simple timeout techniques and assures the UI thread is properly shared between user interactions & warmup and hence making the browser always responsive.

CacheWarmer also detects the availabilty of Web Workers and uses a worker thread to achieve JS multi-threading without interfering with UI responsiveness. With more browsers supporting workers that would be an ideal elegant solution going forward. Please refer to webworker.js for more details.

Functions in CacheWarmer are triggered only when an idle check passes and this idle check function is abstracted out in the utility to be overridden by the implementing application (as the perception of idleness is different for
different applications).

The CacheWarmer has 3 default properties which can be overridden by the application

1. timeout - 50 ms, all function in CacheWarmer queue are time sliced with 50ms intervals
2. isIdle - Abstract function which always returns true, needs to be overridden by the implementer
3. iterations - 2, the max number of iterations the utility will try if isIdle function returns false
4. avoidWorker - false, Flag to indicate that Web Workers should NOT be used

Usage

The complete usage and demostration of cachewarmer is illustrated in dashboard.html (https://github.com/senthilp/cachewarmer/blob/master/dashboard.html). It also provides an interactive tool to play arround the utility

Notes

1. CacheWarmer is loosely based on YUI Async Queue http://developer.yahoo.com/yui/3/async-queue/
2. Webworkers support is TODO action item in the utility
3. The CacheWarmer is no guaranteed to run always. When the idle check fails over all iterations then the cachewarmer will be stopped and queue cleared